Gage control system and method for tandem rolling mills

ABSTRACT

Gage control system and method for tandem rolling mills wherein the roll force or roll gap on all stands in the mill is maintained constant. In the preferred embodiment of the invention, constant roll gap is maintained in the first stand while constant roll force is maintained in all succeeding stands except, possibly, the last stand where measured final output gage is the controlling parameter.

United States Patent [191 Connors et al.

GAGE CONTROL SYSTEM AND METHOD FOR TANDEM ROLLING MILLS Inventors: John ,I. Connors, 5060 Elmcroft Ct.,

Clarence, NY. 14031; Thomas J. Dolphin, 451 Old Greenbriar Rd.; John W. Cook, 84 Pin Oak Dr., both of Willamsville, NY. 14221 Filed: Sept. 29, 1972 Appl. No.: 294,728

US. Cl 72/8, 72/16, 72/205 Int. Cl B21b 37/02 Field of Search; 72/8, 11, 10, 16, 205

References Cited UNITED STATES PATENTS 10/1970 Dunn 72/8 [451 May 7,1974

4/1970 Silva 72/8 5/1962 Schwab 72/205 X Primary ExaminerMilton Mehr Attorney, Agent, or Firm-R. G. Brodahl [5 7] ABSTRACT Gage control system and method for tandem rolling mills wherein the roll force or roll gap on all stands in the mill is maintained constant. In the preferred embodiment of the invention, constant roll gap is main- 11 Claims, 3 Drawing Figures GAGE TENSION TENSION TENSION TENSION CONTROL CONTROL CONTROL CONTROL CONTROL GAGE TEN TEN TEN TEN 5i REF REF P REF REFl REF l F SPEED SPEED C3\ SPEED sPEEo SPEED CONTROL CONTROL CONTROL CONTROL v CONTROL G GE GAGE REF. CONTROL- MASTER SPEED CONTROL PATENTEDm nan j 3 08. 58

SHEET 2 BF 2 6 TENSION A A A A A CONTROL ROLL- FORCE REFERENCE L02 XK TRANS- DUCER TENSION TENSION ah- REFERENCE 32 CONTROL CONTROL Fly. 3 ROLL GAP REFERENCE GAGE CONTROL SYSTEM AND METHOD FOR TANDEM ROLLING MILLS BACKGROUND OF THE INVENTION In the past, it has been common to control the gage of strip material passing through a tandem rolling mill by adjusting the first stand screwdown while simultaneously controlling the interstand tension in the strip ment tend to minimize gage deviations introduced by the mill itself, no attempt is made in prior art systems of this type to further reduce the percent deviation in gage from the desired value below that existing at the output of the first stand under control of the entry automatic gage control system. That is, if the gage has 1 percent deviation out of the first stand, the gage deviation will be 1 percent out of all succeeding stands up to at least the next to the last stand.

SUMMARY OF THE INVENTION In accordance with the present invention, a gage control system for a tandem rolling mill is provided wherein load cell means .are operativcly associated with each of at least those stands in the mill intermediate the first and last stands for producing an electrical signal for each stand which varies as a function of the roll force exerted by that stand. Screwdown means are provided for each stand, which screwdown means may be of the mechanical type or, preferably, of the hydraulic cylinder type. Further means are provided for each of the intermediate stands and responsive to the electrical signal produced by its associated load cell means for adjusting the screwdown means to maintain constant a characteristic of the rolls in relation to the strip being rolled, assuming that interstand tension remains constant.

As will be seen, this characteristic which is maintained constant may be roll force or roll gap. In the preferred embodiment of the invention, an attempt is made to maintain a constant roll gap on the first stand; while constant roll force is maintained'on all succeeding stands, including the last stand. The roll force on the last stand, however, can be varied depending upon a deviation in actual measured output gage from the desired output gage.

On each stand, the roll force or roll gap control comprises an inner loop whose-reference signal can be modified by an outer loop responsive to either interstand tension or gage. The outer loop is responsive to gage on the first stand; is responsive to tension on the intermediate stands; and is responsive to tension and/orfinal output gage on the last stand. If interstand tension or gage varies, so also will the inner loop reference signal and, hence, the roll force or gap.

The above and other objects and features of the invention will become apparent from the following detailed description taken in connection with the accompanying drawings which form apart of this specification, and in which:

FIG. 1 is a block schematic diagram of one embodiment of the invention wherein constant roll gap is maintained on the first stand of a rolling mill and constant roll force on succeeding stands; FIG. 2 is an illustration of a typical operational amplifier utilized in the invention for combining signals proportional to actual tension, roll force, or roll. gap and comparing them with a reference signal; and

FIG. 3 illustrates an alternative embodiment (only one stand) of the invention wherein constant roll gap is maintained on stands succeeding the first stand in a tandem rolling mill.

With reference now to the drawings, and particularly to FIG. 1, the system shown includes a five-stand tandem rolling mill including stands S1, S2, S3, S4 and S5. Each-stand includes a pair of work rolls l0 and 12 between which strip material 14 being rolled passes, together with a pair of backup rolls, not shown. The strip issuing from the last stand S5 is wound on a coiler 15. The rolls of each stand are driven by means of drive motors M1, M2, M3, M4 and M5 each controlled by speed control circuits Cl, C2, C3, C4 and C5, respectively. The speed control circuits cl-CS, in turn, are

connected to a master speed controller 20 which establishes a nominal or desired speed for each of the stands in the mill to achieve a desired gage reduction. In this -respect,-and since each of the stands in the mill is reducing the strip in thickness, the speed of the strip material issuing from any stand must be greater than that entering the stand in accordance with the constant volume principle. Accordingly, the speed of stand S2 must be greater than that of stand S1; the speed of stand S3 must be greater than that of stand S2; and so on the speed of stand S5 being the greatest.

In the embodimentof the invention shown herein, the chocks supporting the rolls in each stand are loaded by means of hydraulic cylinders H1, H2, H3, H4 and H5, respectively. That is, the hydraulic cylinders Hl-H5 provide the necessary roll force to reduce the strip 14 in thickness. While only one cylinder is shown for each of the standsin the schematic illustration given, it will be understood that in actual practice there are hydraulic cylinders operating on two-chocks at either side of the mill. It is, of course, possible to use a mechanical screwdown mechanism or a wedge-type control to effect somewhat the same results; however,

The thickness of strip material passing through the first stand S1 is measured by means of an X-ray gage 22 or the like. Gage 22 produces an electrical signal proportional to the actual gage of the strip material 14 between stands S1 and S2; and this signal is applied'to a gage control circuit 24 where it is compared with an electrical signal on lead 26 proportional to desired exit gage from stand 51. If the actual gage does not match by the hydraulic cylinder H1 to thereby correct for an off-gage condition until the actual measured gage as detected-by gage 22 matches the desired gage signal on lead 26.

Between successive ones of the stands are tensiometers T1, T2, T3 and T4'which measure tension in the strip material between each set of stands. The tensiometer T1, for example, measures the tension between stands S1 and S2 and produces an electrical signal proportional thereto. This tension signal from tensiometer T1, for example, is compared with a tension reference signal on lead 32 in tension control circuit TC2. If the actual tension signal from tensiometer T1 does not match the tension reference signal on lead 32, then an error signal will be produced on lead 34 which is applied to a roll force control circuit RF2.

On each of the stands 51-85 is a load cell or strain gage LCl, LC2, LC3, LC4 or LCS which measures the actual roll force exerted by the rolls 10 and 12 in each one of the stands. In the case of stand S1, the electrical signal produced by load cell LC 1 is multiplied by a factor K in multiplication circuit 36 to derive a signal on lead 38 which is proportional to the gap between the rolls I and 12. That is, in accordance with Hookes law, multiplication of the force exerted by the rolls times a constant, K, gives roll displacement or roll gap. This is compared in the roll gap control circuit 30 with a roll gap reference signal on lead-40 which is proportional to the desired roll gap of stand S1 to achieve a predetermined gage. Assuming that the signal on lead 38 prpportional to actual roll gap is not equal to the roll gap reference signal on lead 40, then the roll gap control circuit 30 will produce an error signal which, through appropriate hydraulic controls, not shown, will increase or decrease the pressure exerted by the cylinder H1 to increase or-decrease the roll gap of stand S1 until the reference and actual signals are the same. Displacement of the piston within cylinder H1 is sensed by a suitable transducer 42 which produces an electrical signal proportional to the position of the cylinder and, hence, the amount of movement of one roll with respect to the other.

The roll force control system on stands S2-S5 is similar to the roll gap control of stand S1 except that in these cases, the actual roll force signal from load cell LC2 for stand S2, for example, is applied through lead 44 to the roll force control circuit RF2 where it is compared with a roll force reference signal on lead 46. Assuming that the actual roll force signal on lead 44 is not equal to the reference signal on lead 46, and assuming further that no error signal exists on lead 34, then an error signal will be produced at the output of circuit RF2 which, through appropriate hydraulic control circuitry, will either increase or decrease the pressure exerted by the cylinder H2 until the desired and actual roll force signals are the same. Instead of using a load cell such as cell LCl, it should be understood that the inner roll gap loop can be responsive to direct measurement of roll gap such as an LVDT device.

Stands S3, S4 and S have similar roll force control circuits RF3, RF4 and RF 5, respectively. Stands S3 and S4 operate in the same manner as stand S2 with the output of the tension control circuit TC3 or TC4 changing the reference to the roll force control circuit RF3 or RF4, assuming that a tension correction is needed. Stand S5 differs somewhat in that final output gage is measured by an X-ray gage 48 or the like and applied to a gage control circuit 50 where it is com-- pared with a signal on lead 52 proportional to desired, final output gage. Applied to the speed control circuit C5 is a signal from the master speed regulator 20 proportional to the nominal speed of stand SS. Assuming that the actual measured gage of the strip material as sensed by gage 48 is equal to that determined by the gage reference signal on lead 52, then the signal from master speed regulator 20 will control and will cause the speed control-circuit C5 to drive stand S5 at the nominal speed determined by regulator 20. If, however, actual measured output gage and desired gage as represented by the signal on lead 52 are not the same, then the signal to speed control circuit C5 will be varied to either increase or decrease the speed of stand S5. This increases or decreases the tension between stands S4 and S5 to effect a gage correction.

In the system shown in FIG. 1, final gage is controlled by controlling the speed of stand S5; while S4-S5 tension is controlled by stand S5 roll force. It should be understood, however, that final gage control can be by way of 54-85 tension; while tension control is by way of stand S5 speed. Alternatively, final gage control can be by way of stand S5 roll force; while tension control is by way of stand S5 speed.

From the foregoing, it can be seen that each of the stands includes an innercontrol loop for maintaining constant either roll force or roll gap, and an outer control loop for maintaining either gage or tension constant. In the embodiment shown in FIG. 1, gage control and roll gap control are used on the first stand S1 while constant roll force control and tension control are used on stands S2-S5. As explained above, however, it is possible, in certain cases, to employ roll force control on the first stand along with the other stands, or roll gap control on all stands.

The manner in which the signals are combined in the inner and outer control loops for the respective stands is illustrated in FIG. 2. It will be assumed that the circuit shown in FIG. 2 is for stand S2. The roll force control circuit RF2 is enclosed by broken lines and comprises a proportional operational amplifier 56 having a resistive feedback path 58. The roll force reference signal on lead 46 is derived through resistor 60 from a po tentiometer 62. In this respect, it will be appreciated that the position of the movable tap on potentiometer 62 determines the desired roll force for stand S2. This can be accomplished manually or, in certain cases, can be accomplished by way of computer control. Applied to the other input of the operational amplifier 56 through resistor 64 is the roll force signal from load cell LC2 on lead 44. This is combined with the tension control signal from tension control circuit TC2 through resistor 66. Assuming that tension is maintained constant at the desired value as determined by the tension reference signal on lead 32, then the only inputs to the operationalamplifier 56 will be that from load cell LC2 and the roll reference signal from potentiometer 62. Again, if these are the same, no output will appear from operational amplifier 56 and no change will be made in the pressure exerted by the cylinder H2. If, however, the actual and reference roll force signals are not the same, then an output will be derived to either increase or decrease the pressure on the rolls of stand S2. The tension control circuit TC2, like the roll force 'circuit RF2,

comprises an operational amplifier, one of whose inputs is a tension reference signal which again can be derived from a potentiometer and the other of which is the signal from tensiometer T1. If these two are the same, no signal is applied to roll force control circuit RF2. However, if they differ, a signal will be applied to the roll force circuit RFZ to produce an output to the cylinder H2 even though the desired and actual roll force signals are the same.

With the arrangement shown, it can be seen that if a gage deviation exists at the output of stand S1, this gage deviation will be corrected, or at least tend to be corrected, by virtue of the fact that the roll force is maintained constant on all succeeding stands in contrast to prior art systems wherein the roll force could vary, depending upon the thickness of the material passing through the rolls.

In FIG. 3, another embodiment of the invention is shown which illustrates only one stand, for example, stand S2. It willbe assumed that all succeeding stands are provided with similar roll gap controls rather than roll force controls as in the embodiment of FIG. 1. Thus, each stand will include a multiplying circuit 70, similar to circuit 36 of FIG. 1, where the roll force signal from a load cell LC2 is multiplied by the constant, K, to produce on lead 72 a signal proportional to roll displacement. This is compared in roll gap control circuit 74 with a roll gap reference signal derived via resistor 76 from potentiometer 78. At-the same time, tension to the second stand is measured by tensiometer T1 and applied to the tension control circuit TC2 along with a tension reference signal on lead 32. Assuming that the actual and desired tension values are not the same, a signal is applied tothe roll gap control circuit 74 where it modifies the reference signal derived from potentiometer 78 in the manner described above in connection with FIG. 2. Again, the position of the piston in cylinder H2 is converted into an electrical signal by means of transducer 80 and applied back to the roll gap control circuit 74 to completethe servo loop.

Although the invention has been' shown and described in connection with certain specific embodiments, it will be readily apparent to those skilled in the art that various changes in form and arrangement of parts may be made tov suit requirements without departing from the spirit and scope of the invention.

What'is claimed is:

1. In a gage control system for a tandem rolling mill having a plurality of successive rolling stands through which strip material passes, the combination of:

load cell means on each of at least those stands of the mill intermediate the first and last stands for producing an electrical signal for each stand which varies as a function of the roll force exerted by that stand,

screwdown means for each stand,

inner control loop means operatively associated with each intermediate stand and responsive to the electrical signal produced by its load cell means for adjusting said screwdown means to maintain constant a characteristic of the rolls in relation to the strip being rolled in the absence of a variation in'the tension in the strip entering a stand, and

outer control loop means associated with each intermediate stand and responsive to a variation in tension in strip entering a stand for varying said characteristic of the rolls until the tension is at a desired value.

2. The combination of claim 1 wherein the characteristic which is maintained constant is roll force.

3. The combination of claim 1 wherein the characteristic which is maintained constant is roll gap.

4. The combination of claim 1 wherein the characteristic which is maintained constant on said intermediate rolls is roll force and including means for maintaining the roll gap of the first stand constant together with means for maintaining the roll force of the last stand constant.

5. The combination of claim 4 including means for modifying the roll gap of said first stand as a function of the gage of the strip material issuing from the first stand.

6. The combination of claim 4 including means for varying the speed of said last stand as a function of the gage of strip material issuing from the last stand.

7. The combination of claim 4 including means for varying the roll force exerted by said last stand as a function of the'gage of strip material issuing from the last stand.

8. In the method for rolling strip material in a tandem rolling mill having a plurality of successive rolling stands through which the strip material passes, the steps of:

measuring the gage of strip material issuing from the first stand in said mill and adjusting the roll gap of said first stand to compensate for variations in gage of strip material issuing from the first stand,

- measuring tension in the strip material between at least some stands succeeding the first stand and controlling via an outer control loop the roll force exerted by the succeeding stands to maintain interstand tension constant, and

simultaneously with the steps enumerated above,

measuring the roll force exerted by said succeeding stands and using the roll force thus measured in inner control loops to maintain roll force constant on said succeeding stands in the absence of a variation in interstand tension.

9. The method of claim 8 including the step of measuring the roll gap of said first stand, and maintaining the roll gap of said first stand constant when the actual gage of strip material 'issuing'from the first standmatches the desired output gage of the first stand.

10. In the method for rolling strip material in a tandem rolling mill having a plurality of successive rolling stands through which the strip material passes, the steps of:

measuring tension in the strip material betweenat least some stands succeeding the first stand and controlling via an outer control loop the roll force exerted by the succeeding stands to maintain inter-- stand tension constant, and simultaneously with the steps enumerated above, measuring the roll force exerted by said succeeding stands and using the roll force thus measured in inner control loops to maintain roll force constant on said succeeding stands in the absence of a variation in interstand tension.

11. In the method for rolling strip material in a tandem rolling mill having a plurality of successive rolling stands through which the strip material passes, the steps of:

measuring tension in the strip material between at least some stands succeeding the first stand and controlling via an outer control loop the roll force 7 8 exerted by the succeeding stands to maintain ininner control loops to maintain the roll gaps con- Sterstand tenslon constant and stant on said succeeding stands in the absence of a simultaneously with the steps enumerated above, measuring the roll force exerted by said succeeding stands and using the roll force thus measured in variation in interstand tension. 

1. In a gage control system for a tandem rolling mill having a plurality of successive rolling stands through which strip material passes, the combination of: load cell means on each of at least those stands of the mill intermediate the first and last stands for producing an electrical signal for each stand which varies as a function of the roll force exerted by that stand, screwdown means for each stand, inner control loop means operatively associated with each intermediate stand and responsive to the electrical signal produced by its load cell means for adjusting said screwdown means to maintain constant a characteristic of the rolls in relation to the strip being rolled in the absence of a variation in the tension in the strip entering a stand, and outer control loop means associated with each intermediate stand and responsive to a variation in tension in strip entering a stand for varying said characteristic of the rolls until the tension is at a desired value.
 2. The combination of claim 1 wherein the characteristic which is maintained constant is roll force.
 3. The combination of claim 1 wherein the characteristic which is maintained constant is roll gap.
 4. The combination of claim 1 wherein the characteristic which is maintained constant on said intermediate rolls is roll force and including means for maintaining the roll gap of the first stand constant together with means for maintaining the roll force of the last stand constant.
 5. The combination of claim 4 including means for modifying the roll gap of said first stand as a function of the gage of the strip material issuing from the first stand.
 6. The combination of claim 4 including means for varying the speed of said last stand as a function of the gage of strip material issuing from the last stand.
 7. The combination of claim 4 including means for varying the roll force exerted by said last stand as a function of the gage of strip material issuing from the last stand.
 8. In the method for rolling strip material in a tandem rolling mill having a plurality of successive rolling stands through which the strip material passes, the steps of: measuring the gage of strip material issuing from the first stand in said mill and adjusting the roll gap of said first stand to compensate for variations in gage of strip material issuing from the first stand, measuring tension in the strip material between at least some stands succeeding the first stand and controlling via an outer control loop the roll force exerted by the sucCeeding stands to maintain interstand tension constant, and simultaneously with the steps enumerated above, measuring the roll force exerted by said succeeding stands and using the roll force thus measured in inner control loops to maintain roll force constant on said succeeding stands in the absence of a variation in interstand tension.
 9. The method of claim 8 including the step of measuring the roll gap of said first stand, and maintaining the roll gap of said first stand constant when the actual gage of strip material issuing from the first stand matches the desired output gage of the first stand.
 10. In the method for rolling strip material in a tandem rolling mill having a plurality of successive rolling stands through which the strip material passes, the steps of: measuring tension in the strip material between at least some stands succeeding the first stand and controlling via an outer control loop the roll force exerted by the succeeding stands to maintain interstand tension constant, and simultaneously with the steps enumerated above, measuring the roll force exerted by said succeeding stands and using the roll force thus measured in inner control loops to maintain roll force constant on said succeeding stands in the absence of a variation in interstand tension.
 11. In the method for rolling strip material in a tandem rolling mill having a plurality of successive rolling stands through which the strip material passes, the steps of: measuring tension in the strip material between at least some stands succeeding the first stand and controlling via an outer control loop the roll force exerted by the succeeding stands to maintain insterstand tension constant, and simultaneously with the steps enumerated above, measuring the roll force exerted by said succeeding stands and using the roll force thus measured in inner control loops to maintain the roll gaps constant on said succeeding stands in the absence of a variation in interstand tension. 